I think neither of these two examples given are in the right timing for phrase 不是 A 就是 B. Usually this phrase is used when put in a much affirmative mood.
Either you or I shall die.
他不是這週 (simplified: 这周) 就是下週飛 (simplified: 飞) 巴西。
He will fly to Brazil either this week or next week.
For your sentences, it will sound more right this way:
明年的中國 (simplified: 国) 之旅，我只打算去一座城市，不是上海就是北京。
I plan to stay in just one city, either Shanghai or Beijing, for my China trip next year.
我們只提供兩種 (simplified: 种) 飲 (simplified: 饮) 品，不是咖啡就是紅 (simplified: 红) 茶。
We offer two sorts of drink only. Either coffee or black tea.
不是 A 就是 B = either A or B
A 或 B = A 或者 B = A 或是 B = A or B